The automotive industry is rapidly innovating to produce greener cars, specifically through use of technology such as electric motors, autonomous driving systems, and active aerodynamics. Active aerodynamics are systems that enhance handling and stability, improve fuel efficiency, and optimize cooling (Refs. 1–3). A notable application of active aerodynamics is in Formula 1® racing, where the drag reduction system (DRS) has led to more exciting races. In this blog post, let’s examine the effects DRS has on a vehicle’s drag and downforce using a simple model created with the COMSOL Multiphysics® software.
Active Aerodynamics in Vehicles
Automotive engineers have long been working on improving the efficiency, speed, and stability of vehicles by fine-tuning the aerodynamics. The two most important aerodynamic metrics in a vehicle are drag and downforce. Drag is a resistive force that opposes the car’s forward motion, reducing its speed and fuel efficiency, while downforce is a vertical force that increases traction by pushing the car toward the ground, improving its stability and handling. Although downforce is generally desirable, generating it often increases drag, creating a tradeoff between speed and stability that designers must balance to see a net improvement in the car’s speed, handling, and fuel efficiency.
Active aerodynamics have transformed automotive design by providing a way to dynamically move components to optimize the drag and downforce in real time and offer a more refined and responsive driving experience. In contrast to traditional passive aerodynamic designs that use fixed components, active aerodynamics feature elements like wings, flaps, and vents that can change position and shape. In road-legal cars, the adjustments are controlled by the car’s onboard computer, which uses real-time data to change the elements based on driving conditions.
The Bugatti Veyron® tail wing rises to generate more downforce at high speeds. Image in the public domain, via Wikimedia Commons.
The first road-legal car to be equipped with active aerodynamics was the Porsche® 959 when it was released in 1986. The technology soon garnered attention and has been pivotal in the design and performance of high-performance cars like the Bugatti Veyron®, the Mitsubishi® 3000GT, and the Pagani Huayra®. Nowadays, active aerodynamics can be found in many road-legal cars, partly to improve fuel efficiency. Cars may be equipped with several active aerodynamic features, including:
- An adjustable rear wing that can rise and change angle depending on the speed and driving mode to balance fuel efficiency, improve performance, and act as an air brake (Ref. 1)
- An adjustable front splitter for enhanced handling (Ref. 1)
- Active air flaps in the front grille that open or close depending on the cooling needs of the engine, thereby reducing drag when cooling is not necessary (Ref. 2)
Another example of innovative active aerodynamics is the drag reduction system (DRS) found in one of the most thrilling high-performance sports today — Formula 1.
The 2015 Malaysian Grand Prix. Image available from Wikimedia Commons, licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
Drag Reduction Systems in Motorsport
DRS is considered an active aerodynamics system because it involves real-time adjustments to the aerodynamic elements of a Formula 1 car. Unlike with the road-legal cars mentioned previously, DRS of Formula 1 cars offers the driver direct control over the system.
In motorsport, DRS is designed to reduce aerodynamic drag on pursuing race cars to facilitate overtaking opportunities during races. By reducing aerodynamic drag, DRS enables cars to gain a significant speed advantage on designated straight sections of a track, also known as “straights”, making it easier to pass the car ahead of them. This helps lead to what many consider more exciting and dynamic races. Therefore, DRS has become a key strategic and tactical element in Grand Prix™ races.
An adjustable rear wing in a Red Bull-sponsored Formula 1 race car. Image available via Wikimedia Commons, licensed under the Creative Commons Attribution 2.0 Generic license.
The core component of DRS is the adjustable wing, which we shall refer to here as the “DRS flap”. The DRS flap can pivot between two positions, one for high downforce and one for low drag. When activated, the DRS flap rises to reduce the angle of attack, which is the angle between the chord line and the oncoming airflow or the trajectory of the car. This change decreases the downforce generated by the wing, which in turn reduces aerodynamic drag. With less drag, the car experiences less air resistance, allowing it to reach higher speeds on a straight. Motorsport engineers estimate the speed increase to be between 10–12 km/h (6.2–7.5 mph) during DRS operation.
DRS is designed to be used only on designated straights where overtaking is most feasible. This is because the reduced downforce also means the car has less grip and is therefore less stable, making it highly unsafe to take corners. When a driver exits a DRS zone and deactivates the system, the DRS flap drops and normal levels of drag and downforce are restored to improve the car’s grip.
The angle of attack of a wing, which plays a crucial role in determining the drag generated by it.
Modeling the Effects of DRS
In the context of automotive design, computational fluid dynamics (CFD) can be employed to simulate and analyze the airflow around a vehicle and predict how changes to the vehicle’s design will impact its aerodynamic performance. CFD modeling is particularly advantageous because it can be used to visualize the airflow pattern, evaluate the aerodynamic forces on various parts of the vehicle, and optimize the design parameters, all while preventing the cost and time associated with expensive trial-and-error procedures. CFD modeling has become a crucial step not only in designing active aerodynamic components but also in several other aspects of automotive manufacturing.
Let’s now go over building a simple model of a DRS flap in COMSOL Multiphysics® to model an adjustable rear wing similar to the one Formula 1 race cars are equipped with. Our goal is to quantifiably inspect the change in aerodynamic drag and downforce on the rear wing during DRS operation to get a better idea of the physics behind the exciting overtakes.
A typical rear wing assembly in a Formula 1 car consists of two wings that span the width of the car. Vertical endplates are attached to the sides of the wings to manage airflow and reduce drag caused by wingtip vortices. In our model, we consider a 2D cross section of a rear wing assembly for simplicity. This enables us to ignore the endplates and consider the cross-sectional geometry of the two wings. We will refer to the upper wing as the “DRS flap” and the lower wing as the “main flap”. (Note that only the upper wing is adjustable.) A NACA 6409 airfoil is used for both of the wings. While the NACA 6409 airfoil does not truly represent the rear wing of a Formula 1 car, this model is intended to simply demonstrate the effect of an adjustable flap on aerodynamic drag and downforce. A gurney flap is fixed to the tail end of the DRS flap and is typically used to increase downforce without significantly increasing drag. The wings are assumed to be perfectly rigid.
Numerical setup of the model consisting of two NACA 6409 airfoils. An inlet and an outlet are defined at the left and right boundaries, respectively. The upper and lower boundaries are defined using the open boundary condition and slip wall condition, respectively.
The Moving Mesh interface in COMSOL® is used to model the actuation of the DRS flap such that it lifts no more than 85 mm from the main flap. This is in accordance with the Formula 1 regulation stating that the DRS flap is allowed to lift a maximum of 85 mm from the main flap. The Turbulent Flow, k-ε interface is used to compute the airflow in the domain. Since we fix the reference frame to the rear wing, an inlet velocity of 90 m/s is defined to model a race car driving at 201 mph on a track. A stationary study is computed to obtain the steady-state flow profile when the DRS is inactive, i.e., when the DRS flap is lowered. A time-dependent study is then performed to simulate the transient effects of the adjustable flap.
Extracting the Metrics
The drag coefficient is a dimensionless number that measures the drag or resistance an object experiences as it moves through a fluid. It represents how smoothly the fluid (air, in our case) flows around the object, with a lower coefficient typically indicating less drag and better aerodynamic efficiency. The drag coefficient, C_d, can be formulated as
where \rho is the fluid density, U_0 is the velocity magnitude, F_x is the x-component of the force on the wings, and A is the cross section of the wings, which can be formulated as
and
where \tau_w = \rho u_\tau^2 is the shear stress at the wall and \bf{u}_t is the tangential velocity. The surface integrations are performed over the boundaries of the wings.
At a zero angle of attack, the downforce can be calculated from \tau_y, which is the vertical component of the shear stress. If the angle of attack is nonzero, we can project the stress onto the direction of lift using the expression -\tau_x \sin \alpha – \tau_y \cos \alpha, where \alpha represents the angle of attack in radians and \tau_x is the horizontal component of the shear stress.
Simulation Results
The animations below show different metrics during DRS operation. For the purpose of this blog post, the DRS is activated two seconds after the study begins and then is active for roughly three seconds. The timing of the operation is somewhat arbitrary in our model but closely resembles a true DRS maneuver in a race.
Animation A shows how the mesh deforms with the movement of the DRS flap. The plot shows how much the DRS flap lifts from the main flap. A 19.5˚ rotation of the DRS flap corresponds to a lift of 84 mm from the main flap, which is within regulation.
Animation A: The simulation results showing the deformation of the mesh elements modeled using the Moving Mesh interface (left) and the position of the DRS flap with respect to the main flap (right).
Animation B shows the velocity streamlines during the operation of the DRS. The plot shows that the maximum velocity of air is lower when the DRS is active. This should not be confused with the velocity of the car, which will be higher when the flap is raised.
Animation B: The simulation results showing the velocity profile and streamlines (left) and the maximum velocity in the domain (right).
Animation C shows that the drag coefficient of the rear wing decreases by up to 27.1% when the DRS is activated. The downforce on the flap is also plotted, showing a decrease by up to 23.6% when the DRS is activated.
Animation C: The simulation results showing the drag coefficient and downforce during DRS operation.
Although these results are from a model built with an arbitrary geometry, the real-life application of DRS can have substantial effects on drag. For instance, in Formula Student competition vehicles, DRS can reduce drag by up to 78% (Ref. 4). This reduction can vary based on the car’s speed, the aerodynamic setup, the specific DRS design, and the track layout.
Summary of Modeling Benefits
Active aerodynamics provide significant benefits to high-speed cars and have gained popularity in road-legal vehicles as well. The model featured here demonstrates the effects of an adjustable flap on drag and downforce using a simple cross-sectional 2D representation of the rear wing assembly of a race car. Such simple models can aid with understanding the principles of CFD and showcase the exciting applications of aerodynamics. The model setup featured here can also be extended to model structural deformation of the flaps as they respond to pressure stresses using the Fluid-Structure Interaction multiphysics coupling in COMSOL®.
Studying the aerodynamics of a car using a COMSOL model.
Try It Yourself
To study the effects an adjustable flap has on drag and downforce, click the button below! The button will take you to the model that corresponds with this blog post.
References
- J. Piechna, “A Review of Active Aerodynamic Systems for Road Vehicles,” Energies, 2021.
- C. Pfeifer, “Evolution of active grille shutters,” SAE Technical Paper, 2014.
- W. Yu and G. Wei, “A Review of the influence of active aerodynamic tail on vehicle handling stability,” Journal of Physics: Conference Series, 2021.
- R. Loução, D. Gonçalo, and M. Mendes, “Aerodynamic study of a drag reduction system and its actuation system for a formula student competition car,” Fluids, 2022.
- J. Noble, “How F1’s new active aero will work in 2026,” Autosport, 2024.
Further Learning
To learn more about some of the topics discussed here, check out these articles on the COMSOL Blog:
- Studying the Airflow Over a Car Using an Ahmed Body
- Simulating Wind Load on a Sports Car’s Side Door and Mirror
- How Do I Compute Lift and Drag?
- Optimize NACA Airfoil Designs with a Simulation App
The information presented in this article is relevant during the 2024 motorsport season. DRS in Formula 1 is set to be replaced in 2026 by a more involved active aerodynamics system that enables more dynamic adjustments (Ref. 5). Formula 1 racing is an ever-changing and innovative sport, and the technologies discussed here may be obsolete in the future. The article is intended to be a demonstration of the power of simulation in understanding the principles of aerodynamics rather than a guide to the rules of motorsport. Formula 1 is a registered trademark and Grand Prix is an unregistered trademark of Formula One Licensing B.V. Bugatti and Veyron are registered trademarks of Bugatti International S.A. Huayra is a registered trademark of PAGANI S.p.A. Mitsubishi is a registered trademark of MITSUBISHI JUKOGYO KABUSHIKI KAISHA. Porsche is a registered trademark of Dr. Ing. h.c. F. Porsche Aktiengesellschaft.
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